Embodiments described herein generally relate to systems and methods for measuring forces acting on a downhole tool.
The pressure of a fluid within the bore of a downhole tool is oftentimes determined by drilling or otherwise forming a radial penetration in the tool and inserting a pressure gauge into the bore via the penetration. When a penetration is neither acceptable nor desirable, the bore pressure is determined by measuring the deformation of the tool. For example, when the bore pressure is greater than the pressure outside of the tool, the tool tends to swell or expand radially outward. This causes the length of the tool to decrease (as a result of Poisson's effect). When the bore pressure is less than the ambient pressure, however, the tool tends to compress or contract radially inward. This causes the length of the tool to increase (as a result of Poisson's effect). This method for measuring the fluid pressure within the bore of the tool is more accurate when there is no axial load on the tool.
Axial loads on the tool, however, can affect the measurement of the fluid pressure within the bore. For example, the length of the tool increases when the tool is under a tension load. This causes the tool to compress or contract radially inward. Conversely, the length of the tool decreases when the tool is under a compression load. This causes the tool to swell or expand radially outward. Thus, an axial load on the tool will affect or interfere with the measurement of the fluid pressure in the bore, and vice versa. This interference is known as “cross-talk.”
What is needed, therefore, is an improved system and method for measuring the bore pressure and the axial load placed on a downhole tool.